1. Field of the Invention
The present invention relates to an exposure head used for an instant printer and so forth.
2. Description of the Related Art
An instant printer built in an electronic still camera obtains a subject image by exposing an instant film with an exposure head utilizing a semiconductor light source of LEDs, a laser and so forth. Incidentally, the LEDs emit the light of red, green and blue. On the instant film, is recorded a subject obtained through a taking lens. In the case of the exposure head, the light emitted from the LED and the laser is condensed on the instant film by using a lens system of a condenser lens and so forth. Colors are controlled every dot. When the lens system is used for the exposure head, there arises a problem in that the exposure head becomes large. Further, in this instance, an amount of the light is reduced at the time of light transmission. Thus, there arises another problem in that it is required to secure sufficient exposure duration by slowing down a printing speed, in order to gain enough amounts of the light.
As to a method for solving the above problems, Japanese Patent Laid-Open Publication No. 10-76706 discloses a small-sized exposure head in which a condenser Lens is not used. This exposure head comprises a light-source portion, a front portion, and a light shielding portion. The front portion is formed with an opening for irradiating exposure light, which is emitted from a semiconductor light source, to a photosensitive material. The light shielding portion is formed with an opening for containing the semiconductor light source. The front portion is adapted to face the photosensitive material. By virtue of this, the light emitted from the light source is directly irradiated to a photosensitive surface of the photosensitive material. In this way, it is possible to form an image by using the high-intensity exposure light whose attenuation is small.
However, in the above-mentioned exposure head, the opening formed in the front portion is smaller than the opening formed in the light shielding portion. Due to this, there arises a problem in that the light emitted from the light source can not be efficiently used. As a method for solving this problem, it may be considered to employ a photosensitive material having high sensitivity. However, using the photosensitive material of high sensitivity causes an increase of cost. Meanwhile, since this exposure head does not use a lens system, a depth of focus is shallow. Thus, when a distance between the photosensitive material and the exposure head is long, there arises a problem in that contrast is lowered.
In view of the foregoing, it is a primary object of the present invention to provide an exposure head and a producing method therefor in which an amount of light emitted from a light source is efficiently used without using a lens system.
It is a second object of the present invention to provide an exposure head and a producing method therefor in which high-quality printing is performed by making a depth of focus deep.
In order to achieve the above and other objects, the exposure head according to the present invention comprises a plurality of light emitting elements and a light guiding member for surrounding each of these elements. The light emitting elements are disposed at same intervals to form an image on a photosensitive material. The light guiding member is attached to the light emitting element so as to surround an optical axis thereof. Light of the light emitting element is uniformly applied to a photosensitive surface of the photosensitive material by means of the light guiding member. At the same time, a part of the light of the light emitting element is reflected on an inner wall of the light guiding member. Owing to this, the lights of the adjacent light emitting elements are prevented from overlapping on the surface of the photosensitive material.
In a preferred embodiment, the inner wall of the light guiding member has at least two kinds of reflectance, namely low reflectance and high reflectance. A cross section of the light guiding member perpendicular to the optical axis is preferable to be a square shape or a circular shape. The inner wall of the light guiding member is constituted of a first low-reflection area, a high-reflection area, and a second low-reflection area. These areas are arranged from a side of the light emitting element toward the photosensitive material. The light guiding member is preferable to be disposed such that a middle point between the light emitting element and the photosensitive material is positioned within the high-reflection area.
In another embodiment, the inner wall of the light guiding member is slanted in an optical-axis direction thereof. The cross section of the light guiding member perpendicular to the optical axis is formed so as to become smaller gradually toward a light irradiation opening. In this instance, a slant angle xcex8 of the inner wall is preferable to be within a range of 1xc2x0xe2x89xa6xcex8xe2x89xa63xc2x0. It is further effective that the inner wall of the light guiding member is formed from a material having the reflectance of 50% or more.
As to a producing method for the light guiding member whose inner wall is constituted of at least two kinds of reflectance, there is a method in which masking is performed for the low-reflection area of the light guiding member. Except a portion of masking, plating or deposition is carried out to form the high-reflection area.
According to the exposure head of the present invention, it is possible to obtain a large amount of the light without using a condenser lens. Moreover, the light of the light emitting element may be effectively used so that a picture print having high quality may be obtained without using a photosensitive material having high sensitivity. Further, it is possible to realize the exposure head in which the depth of focus is deep. Owing to this, positional management of the photosensitive material may be easily executed, and costs of the printer itself may be reduced.